This project is for an investigation of the role of periodic clinical, roentgenologic, sigmoidoscopic in colonoscopic biopsy and cytologic collections, and plasma and colonic CEA as to their predictive value in the detection of colonic carcinoma and ulcerative colitis. It employs a skilled team consisting of gastrointestinal clinicians, a pathologist, a radiologist, gastrointestinal morphologist, a gastroenterologist skilled in radio-immune assay, and a cytologist. New features of this project include 1) the addition of colonoscopic observations, biopsy collection, and cytology collection 2) electron microscopic studies to more accurately define stages of differentiation of precancer 3) correlation of serial serum and colonic CEA determinations with the above observations 4) organ culture and electron microscopic studies to further search for etiologic clues in ulcerative colitis.